for loops in python require either iterable or iterator object.as such the following two for loops produce the same result

Question

for loops in python require either iterable or iterator object.as such the following two for loops produce the same result.

list = [1,2,3,4,5,6,7,8,9]
for i in iter(list):
    print(i)
print(end = "\n")
for i in list:
    print(i)

both the for loops prints out 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 my question is why we have these two forms ? why don't we use the second form only( directly iterating over the iterable than creating iterator from it and iterating )?

I have not used form #1 on lists in 20 years of Python programming. So, who exactly is "we"? — Klaus D., Apr 03 '21 at 11:56
`iter` sometimes performs a useful role, but it is redundant here since `for` essentially calls `iter` anyways. — Mateen Ulhaq, Apr 03 '21 at 12:00
Related https://stackoverflow.com/questions/18809475/iterator-vs-iterable, https://stackoverflow.com/questions/9884132/what-exactly-are-iterator-iterable-and-iteration — snakecharmerb, Apr 03 '21 at 12:04

score 4 · Answer 1 · answered Apr 03 '21 at 12:00

4

You can use iter for this type of use case

arr = [1,2,3,4,5,6,7,8,9]
  
iter_arr = iter(arr)
  
print(next(iter_arr)) # 1
print(next(iter_arr)) # 2
print(next(iter_arr)) # 3
next(iter_arr)
print(next(iter_arr)) # 5

answered Apr 03 '21 at 12:00

Kamil Kozioł

194
7

score 0 · Answer 2 · answered Apr 03 '21 at 12:24

iter() returns an iterable object which can be iterated one at time. Similar functionality can also be achieved by using yield keyword. This helps to reduce overhead of memory allocation.

Input:

res = [1,2,3,4,5]

Using iter():

iter_obj = iter(res)

print(next(iter_obj))
print(next(iter_obj))
print(next(iter_obj))
print(next(iter_obj))
print(next(iter_obj))

Using Yield:

def f(res):
    for i in res:
        yield i

for i in f(res):
    print(i)

Output:

for loops in python require either iterable or iterator object.as such the following two for loops produce the same result

2 Answers2